The NSA has apparently figured out a secret way to tap into the links between Internet users and Google and Yahoo data centers overseas. The companies say they didn't give the NSA permission, and they are angry. Because the data centers are located outside the United States, the NSA may not be bound by the same laws that govern domestic surveillance. The case shows how difficult it is for policymakers and legislators to oversee NSA surveillance activities.

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From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

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And I'm Audie Cornish. We begin this hour with yet another example of how the National Security Agency can scoop up and search personal data that we thought was private. Once again, the disclosures come from NSA documents taken by former contractor Edward Snowden. The Washington Post is reporting that some of those documents show the NSA has been able to secretly tap into the links that connect Internet users to Google and Yahoo data centers overseas.

Here to make sense of the story is NPR's Tom Gjelten. And Tom, first, let's break down this latest disclosure. It's very technical. And I want to start - what, exactly, are these data centers?

TOM GJELTEN, BYLINE: Well, Audie, that's where Google and Yahoo store all their data. Remember, when you do an Internet search, they record it, they want to know what you're looking for. That's important to advertisers, for example. When you send an email - whether it's text or photo or video - they keep a copy of that. All in all, this adds up to an enormous amount of data, and it's stored in these data centers. That's the cloud. Some of the data centers are here in the U.S.; some of them are overseas. This story's about the ones that are overseas.

CORNISH: And so how does the NSA actually get to those ones overseas?

GJELTEN: Well, the Post is reporting that the NSA and its British counterpart agency have figured out a way to tap directly into those overseas Google and Yahoo data centers or into the links between them. Google and Yahoo try to protect the data as it travels back and forth along these links. But apparently, the NSA and their British colleagues have found ways to tap into those links directly so they can grab that data. They can grab the emails, the Google documents, the Internet search records, and hold that data for a few days while the NSA searches to see if there's anything in there that interests them.

CORNISH: Now, some elements of this may sound familiar to people from earlier stories. What's different?

GJELTEN: You're right. We already knew the NSA could search data stored in this country, but it had to be searching for something in particular, some targeted person or address with a foreign connection. And the companies were required to cooperate. This is sneakier. The companies didn't know about it. And because it's overseas, the rules are a lot looser.

CORNISH: So what's been the reaction from Yahoo, from Google?

GJELTEN: They're furious. The Google lawyer says they're outraged by this. They've put a lot of effort into trying to keep this data private. The Post reporter said that when they showed some Google engineers a drawing - apparently, by an NSA technician - showing where the intercepts could take place, the Google engineers exploded with a profanity.

CORNISH: Now, give us some context here. Given all the other ways it's collecting communications around the world, why does the NSA go to such lengths to get this kind of data?

GJELTEN: Well, basically, they want to satisfy their customers. For example, if the president asks a question about something happening somewhere, the NSA wants to have the answer. And in this day and age, with so much happening in the digital space, the answers the NSA probably needs are hiding somewhere out there in the cloud. They feel they have to be able to look there.

CORNISH: Finally, Tom, what are some of the lessons here for, say, policymakers, lawmakers who essentially set the rules for what the NSA can and can't do?

GJELTEN: That's a really important question, Audie. From the beginning of the NSA, there's been one hard and fast rule. You cannot spy on Americans without a court order. What the policymakers and legislators have to do now is figure out how you enforce that rule, given that communications are global, networks are global, links are everywhere. It's really, really hard to draw a line between the communications of U.S. persons, and the communications of non-U.S. persons.

In this case, for example, you may have Americans whose communications are going overseas through those data centers. The Post says, it appears the NSA is now in position to search Americans' communications overseas without the restrictions they would face in this country. So how you provide the oversight in this situation, that's the key. Lots of questions the courts and Congress have to deal with.

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